DK2032864T3

DK2032864T3 - DISC AND THEREFORED SCREW CONNECTION

Info

Publication number: DK2032864T3
Application number: DK07786771.1T
Authority: DK
Inventors: Erich Palm
Original assignee: Sfs Intec Holding Ag
Priority date: 2006-06-26
Filing date: 2007-06-20
Publication date: 2018-07-30
Also published as: WO2008000668A1; US7955036B2; EP2032864B1; CA2642484A1; TR201808017T4; CA2642484C; PL2032864T3; US20090196686A1; EP2032864A1; DE102006029253B3

Description

The invention refers to a screw connection between a screw and a workpiece, wherein the screw has a shaft which is provided with a thread and has an unthreaded shaft section at its end adjacent to the head, wherein a washer is arranged between the head of the screw and the workpiece, wherein the washer has a bore receiving the screw and is spatially deformed about an axis extending diametrically through the bore in such a manner that the washer is angled about the diametric axis so that an angular crown line is parallel to the axis and the angled washer has an operational thickness greater than the initial thickness of the washer, and wherein the washer is made from a material selected such that the washer is plastically deformable when the threaded assembly is made. A threaded assembly according to the preamble of claim 1 is known from document GB-A-1 493 220. This known threaded assembly is made with a washer which is plastically deformed when the screw is tightened. The plastic deformation of the washer is used to deflect a leg attached to each end of the washer into a shoulder of the head of the screw. In this way, the washer is attached to the head through the legs and cannot fall away from the head when untightening. This reduces the risk that a washer falling off results in a short circuit in an electrical distributor. In this well-known threaded assembly, the workpiece is a terminal block that must be very stable and thick for safety reasons so that no deformation is possible therein. A spring washer is located between the screw head and the washer. However, this should mainly serve as a reverse rotation protection for the screw. A known washer that could be used for a threaded assembly of the type mentioned above is, for example, a corrugated washer. It is used in a threaded assembly to secure the screw against loosening and reverse rotation. Such a corrugated washer is made of spring steel and is elastically deformed during the creation of the threaded assembly, i.e. during the tightening of the screw. Due to the elastic deformation of the corrugated washer, the finished threaded assembly remains prestressed by a spring force acting in the direction of the screw axis. If a potentially existing play is to be compensated in a threaded assembly, washers are usually used which have a defined thickness corresponding to the play to be compensated. Corrugated washers or the like have only a small thickness and their suitability to be used to compensate play in addition to their function of preventing reverse rotation is therefore very limited. A threaded assembly in which no plastically deformable washer is used is known from DE 197 18 712 Cl. A similar threaded assembly is known from, document U.S. 2,321,379, wherein in this case the screw is not provided with a holeforming or drilling tip but merely has an end of the shaft that is slightly tapered. In both cases, the workpiece consists of two thin plates, which can be clamped towards each other in a secure manner with the help of the screw. Due to the fact that an unthreaded shaft section is formed between the head and the thread provided on the shaft being of the same size or slightly smaller than the thickness of the two thin plates to be connected to each other, the screw can be overtightened after the final setting. A tight assembly of the thin plates forming the workpiece without the screw still being able to untighten by rotating reversely is only ensured if no play exists between the head of the screw and the workpiece. For this purpose, the thickness of the workpiece must be precisely equivalent to the length of the unthreaded shaft section or may be only slightly greater than the length of the unthreaded shaft section. In general, in the assembled position, the two thin plates shall be held in a tightly compressed fashion. If one of the two thin plates is too thin or only a screw is available, the unthreaded shaft section of which is too long for the existing thickness of the workpiece, play occurs with no possibility for compensation being provided in such a threaded assembly. Due to its small thickness, a lock washer such as a corrugated washer would be suited to a limited extent only.

The document EP 0 556 438 A1 describes a screw with an elastically deformable washer for creating a threaded assembly. The elastic restoring force of the washer is used to create a fixed assembly. Even with such a washer, compensation of play is possible to a limited extent only.

The object of the invention is to design a threaded assembly of the type mentioned at the beginning such that any play can be compensated over an expanded range and/or that protection against loosening of the screw due to reverse rotation can be ensured therewith.

This object is achieved by the invention, based on a threaded assembly of the type mentioned above, in that the workpiece consists of at least one and preferably a plurality of thin plates, that the shaft has a hole-forming or hole-drilling tip at its free end facing away from the head, and that the length of the unthreaded shaft section is smaller than the sum of the thickness of the workpiece and the operational thickness of the washer and substantially is not smaller than the sum of the thickness of the workpiece and the initial thickness of the washer.

In the threaded assembly according to the invention, in which the screw has an unthreaded shaft section, the thickness of the workpiece may be smaller than the length of the unthreaded shaft section in a wide area. Nevertheless, a tight connection is achieved without any play between the head of the screw and the workpiece because due to the selection of the length of the unthreaded shaft section according to the invention, sufficient possibilities to compensate play are provided for a wide range of play. The above-mentioned tight connection without any play ensures the intended protection against any loosening of the screw caused by reverse rotation. When creating the threaded assembly, the screw is simply tightened until the workpiece is located in the unthreaded shaft section such that the screw can spin. From that time on, no additional deformation force acts upon the washer. Rather, it maintains its plastic deformation obtained at that time, which precisely compensates the play existing between the work piece and the head of the screw. This possibility for compensation applies to a range extending downwards up to a play equivalent to the original thickness of the washer, thus the thickness of the washer in the state prior to being angled. In this case, the washer is being plastically deformed until the workpiece is situated in the unthreaded shaft section and the washer is flattened again. Of course, in the above-described applications, the washer according to the invention must have sufficient pull-out strength in the thin plates to be connected, i.e. the force for pulling it out of the workpiece must be greater than the force to be applied for plastically deforming the washer. If the thin plates are steel sheets or the like, usually sufficient pull-out strength is provided anyways .

In the threaded assembly according to the invention, the washer consists of a material that is selected in such a way that the washer is plastically deformable when the threaded assembly is created and the pull-out force of the screw from, the workpiece, which has at least one thin plate, is greater than the force that must be applied to plastically deform the washer.

With the threaded assembly according to the invention, the washer can be used in such a way that after setting of a screw having an unthreaded shaft section, there is no more play between the head and a workpiece to be fastened to a surface or the like if the end of the screw is at a stop or if the drive of a screw setting device is switched off by a depth stop. The washer is plastically deformed during setting and thus eliminates any play between the workpiece and the screw head, even with originally large play. The angled shape of the washer makes it possible to compensate for play in a very large range.

If, in one embodiment of the threaded assembly according to the invention, the bore of the angled washer is conical, the washer can be used in conjunction with screws in which the shaft of the screw has a conical connection to the head of the screw.

If, in another embodiment of the threaded assembly according to the invention, the washer is angled transversely to the diametric axis by a distance which is at least equal to the initial thickness of the washer, the washer is particularly suitable in cases in which small play is to be compensated.

If, in another embodiment of the threaded assembly according the invention, the angle by which the washer is angled is less than 180° and greater than or equal to 90°, the washer in the threaded assembly according to the invention provides a compensation possibility for play which can vary within a considerable range.

If, in another embodiment of the threaded assembly according to the invention, the washer is circular in shape, the washer can be easily manufactured from a flat washer or the like, whereby it must only be ensured that it is made from an appropriately plastically deformable material.

If, in another embodiment according to the invention, the washer has the shape of a polygon, the washer can be produced just as easily without assuming a flat, circular washer blank.

If, in another embodiment of the threaded assembly according to the invention, the material of the washer is carbon steel, i.e. unalloyed steel, the washer is made of a material which is readily available and whose plastic deformability is ideally suited for clearance compensation.

If, in another embodiment of the threaded assembly according to the invention, the thread of the screw is self-tapping or self-forming, the threaded assembly can be created in a simple manner without a threaded hole being made in the w o r kp i e c e b e f o r e h a n d .

If, in another embodiment of the threaded assembly according to the invention, the diameter of the unthreaded shaft section is at most, egual to the core diameter of the thread, the threaded assembly can be created in a simple manner without wasting part of the force available for plastically deforming the washer in order to pull the unthreaded shaft section through a hole that is too narrow.

If, in another embodiment of the threaded assembly according to the invention, the shaft of the screw has a conical connection to the head of the screw, this connection can be received by the bore of the washer, which will also be conical, at least by the bending the washer.

If, in another embodiment of the threaded assembly according to the invention, the bore of the washer is adapted to the conical connection of the shank, at least in the unassembled state of the washer, the washer has substantially no axial play with respect to the unthreaded shaft section of the screw even if the finished threaded assembly is finished.

In the following, exemplary embodiments of the invention are described in greater detail with reference to the drawings. In the figures:

Fig. 1 shows a washer blank that can be used for a washer according to the invention,

Fig. 2 shows a threaded assembly according to the invention in a state in which the washer according to the invention has not yet been deformed by tightening the screw,

Fig. 3 shows the threaded assembly according to the invention in a state in which the washer is plastically deformed,, and

Fig. 4 shows a side view of the threaded assembly according to Fig. 3.

Fig. 1 shows an exemplary embodiment of a washer blank indicated by 10. The washer blank 10 is a planar, c.ircular washer provided with a conical bore 12, From the washer-blank 10, through a process of spatial deformation, an angled washer 14 is produced, as shown in Fig. 2. The bending of the washer blank 10 is carried out about at. least one axis 16 extending diametrically through the bore 12, as indicated in Fig. 4 by dotdashed lines. The washer blank 10 could additionally be bent (not shown), e.g., about another diametrical axis extending diametrically through the bore 12 and perpendicular with respect to the axis 16. In this case, the bending around the diametric axis 16 would be carried out such that an angular crown line 18, as can be seen in Fig. 4, is parallel to the axis 16, and further is perpendicular with respect to the diametric axis 16, namely in each of both cases by a distance at least equal to an initial thickness Da of the washer 14, i.e. equal to the thickness Da of the washer blank 10. In general, the angle by which the washer 14 is bent and which for the purpose of the present description is equal to the angle a which the two angular legs of the washer 14 enclose is less than 180° and greater than or equal to 90°. The washer 14 is of a circular shape, but bent abound the diametric axis 16 by the angle a. The same washer 14 as a washer blank is also of a circular shape, but planar. Instead of a circular shape, the washer may also have the form of a polygon provided with a central bore 12, thus e.g., a square shape. By the bending about the diametric axis 16, the washer obtains an operational thickness De with respect to the initial thickness Da, indicated in Fig. 2, which is considerably larger than the initial thickness Da. The washer 14 is made of a material selected such that the washer can be plastically deformed during the creation of the threaded assembly,, described here in greater detail with reference to Figs. 3 and 4. Suitably, the washer 14 may be made of soft or unalloyed carbon steel, for example, so that upon application of pressure in the direction of an axis 20, the washer is not deformed elastically but plastically from the status shown in FIG. 2 under load in the direction of an axis 20. By the bending with respect to the initial state shown in Fig, 1, the washer 14 is given the shape of a gabled roof .

In the following, the use of the washer 14 in the threaded assembly generally indicated with 22 in Figs 2-4 is described as an example of use. A, screw 30, the central axis of which is the axis 20, is provided with a shaft 32 and a head 34, The shaft 32 is provided with a thread 36. At its free end, facing away from the head 34, the shaft 32 has a hole-drilling tip 38, which could also be simply a hole-forming tip. The shaft 32 has an unthreaded shaft section 40 at its end opposite the tip between the head 34 and the thread 36. In the exemplary embodiment shown, a work piece generally indicated with 42 consists of two thin plates, namely a plate 42a and a plate 42b, with the latter being thinner than the plate 42a. Suitably, the arrangement of the two thin plates 42a, 42b on top of each other is selected such that the thicker plate 42a is located at the side facing the head 34 of the screw 30, as illustrated in Figs. 2 to 4.

The unthreaded shaft section 4 0 has a length Lg in the axial direction of the screw 30, which in the exemplary embodiment shown is equal to the operational thickness De of the washer 14. According to the invention, the length Lg of the unthreaded shaft section 40 is smaller than the sum of the thickness Dw of the workpiece 42 and the operational thickness De of the washer 14. In any case, the length Lg of the unthreaded shaft section 4 0 should not, be shorter than the sum of the thickness D« of the workpiece 42 and the initial thickness Da of the washer 14 and/or the washer blank 10. With appropriately thin plates 42a, 42b to be connected to each other, this embodiment allows an overtightening of the screw 30 without the torque rising excessively. As soon as the screw 30 is overtightened, the thin plates 42a, 42b are held tightly together, and it is practically impossible for the threaded assembly to be untightened by reverse rotation of the screw 30. This state is shown in Figs. 3 and 4, which will be discussed in greater detail below. If the length La of the unthreaded shaft section 40 is slightly shorter than the sum. of the thickness D« of the two thin plates 42a, 42b and the initial thickness Da of the washer 14, there is also the possibility that the screw 30 can overtighten after the final setting. However, in doing so, it still engages slightly in the underside of the thin plate 42b .

The thread 36 of the screw 30 is self-cutting or selfforming. In the exemplary embodiment described here, the diameter Dg (Fig. 2) of the unthreaded shaft section 40 is equal to the core diameter Eg of the thread 36. The shaft 32 of the screw 30 has a conical connection 33 to the head 34 of the screw 30. At least in its unassembled state, the bore 12 of the washer 14 is adapted to the conical connection 33 of the shaft 32, as indicated in Figs. 2-4, in which the conical connection 33 is received with play in the conical bore 12.

In the following, the setting of the screw 30 is described in greater detail with reference to Figs. 2-4. In the state of the threaded assembly 22, shown in Fig. 2, the angled washer 14 bridges the distance between the top of the workpiece 42 and the bottom of the screw head 34, but is not yet deformed. The operational thickness De of the angled washer 14 is therefore equal to the length Lg of the unthreaded shaft section 40. The screw 30 has previously drilled a hole with the core diameter Dk into the workpiece 42, using its tip 38, and then cut a thread 43 into the workpiece 42, using its thread 36, into which the screw 30 has been screwed until its uppermost thread pitch is at the level of the top of the thin plate 42a and is flush therewith, as shown in Fig. 2.

If screw 30 is now screwed in further, the washer 14 is plastically deformed with increasing feed of the screw 30 into a flattening state and finally reaches the state shown in Fig. 3, in which the uppermost thread pitch of thread 36 exits from the threaded hole in the workpiece 42 at the bottom and is at the level of the underside of the thin plate 42b. From this moment on, the screw 30 can overtighten without any further feed in the direction of axis 20 taking place. At the same time, the plastic deformation of the washer 14 stops, which now maintains the state shown in Fig. 3 and 4. Fig, 3 shows the washer 14 in front view, and Fig. 4 shows the washer 14 in side view. The washer 14, which in Fig. 2 still had the operational thickness De, now has only a considerably smaller thickness Df, with which it compensates for a play of the same size. The angle of the washer 14 in the initial state according to Fig. 2 and the material of the washer 14 at a given initial thickness Da of the washer 14 are selected in relation to the pull-out force of the screw 30 from the workpiece 42 such that the force exerted on the washer 14 by the feed of the screw 30 to plastically deform the same is always less than the pullout force. The preload force exerted on the washer 14 in the state shown in Fig. 3 and 4 is zero as soon as the thread 36 has left the thread engagement with the workpiece 42.

In the prior art, as described above in the documents DE 197 18 712 Cl and U.S. 2,321,379, the aim is to select the total thickness of the thin plates in such a way that it is as equal as possible or only slightly greater than the length of the unthreaded shaft section, so that as soon as the screw overtightens in the plates, the plates are firmly pressed against the underside of the screw head. However, if the thickness of the thin plates varies and axial play occurs between the underside of the screw head and the adjacent thin plate, it is not possible in the prior art to compensate for this play. In the threaded assembly 22 described here, the length Lg of the threadless shaft section 40 is made equal to the operational thickness of the angled washer 14 from the outset, wherein the operational thickness De is necessarily greater than the initial thickness Da of the washer 14. From a comparison of Figs. 2 and 3 it can be seen that the washer 14, with corresponding thickness Dw of the workpiece 42, could be compressed to the thickness Da of the washer 14, wherein Da would then be equal to Df. Preferably, Df should be larger than Da, so that in the case of varying play, greater security is ensured when compensating for the remaining distance between the bottom of the screw head 34 and the top of the workpiece 42 in the state shown in Fig. 3. In the setting state of screw 30 shown in Figs. 3 and 4, the angled disc 14, compared to the state in Fig. 2, has been pressed flat by the thickness Dw of the workpiece 42. The thickness of the workpiece 42 thus determines the greatest possible deformation of the washer 14. The deformation can go so far that the washer 14 finally has a thickness Df, which is equal to the initial thickness Da, as explained above. However, a design in which Df is larger than Da offers more freedom.

In the exemplary embodiment shown, the washer 14 is a circular ring-shaped washer bent about the axis 16. In the state shown in Fig. 2, it has practically only point contact with the top of the workpiece 42 at two diametrically opposite points. If the washer 14 is increasingly flattened by plastic deformation towards the state shown in Figs. 3 and 4, the original point contact on both legs of the washer 14 transitions increasingly into a surface contact, as can be seen in Figs. 3 and 4. In this state, the washer 14 rests fully against the upper side of the workpiece 42 on both sides of the screw 30.

Claims

A screw connection between a screw (30) and a workpiece (42), wherein the screw (30) has a shank (32) provided with a thread (36) and at its end adjacent the head (34) has a thread-free shaft section (40), where between the head (34) of the screw (30) and the workpiece (42) is arranged a disc (14), the disc (14) having a bore (12) which receives the screw (30) ), and about at least one diameter (16) extending through the bore (12) is spatially deformed such that the disc (14) is angled about the diametrical axis (16) such that an angular top line (18) is parallel to the axis. (16) and the angled disc (14) have a functional thickness (De) which is greater than the output thickness (Da) of the disc (14) and wherein the disc (14) consists of a material selected such that the disc ( 14) in the manufacture of the screw connection (22) is plastically deformable, characterized in that the workpiece (42) consists of at least one and preferably several thin sheets is (42a, 42b) that the shaft (32) at its free end away from the head (34) has a hollow or bore tip (38) and that the length (Lg) of the threadless shaft portion (40) is less than the sum of the thickness (Dw) of the workpiece (42) and the functional thickness (De) of the disc (14) and substantially no less than the sum of the thickness (Dw) of the workpiece (42) and the output thickness (Da) of the disc (14).

Screw connection according to claim 1, characterized in that the bore (12) in the angled disc (14) is tapered.

Screw connection according to Claim 1 or 2, characterized in that the disc (14) is angled across the diametrical axis (16) at a distance which is at least equal to the output thickness (Da) of the disc (14).

Screw connection according to any one of claims 1-3, characterized in that the angle a, at which the disk (14) is angled, is less than 180 ° and greater than or equal to 90 °.

Screw connection according to any one of claims 1-4, characterized in that the washer (14) is circular in shape.

Screw connection according to any one of claims 1 to 4, characterized in that the washer (14) is in the form of a polygon.

Screw connection according to any one of claims 1-6, characterized in that the material of the disc (14) is carbon steel.

Screw connection according to any one of claims 1-7, characterized in that the thread (36) of the screw (30) is self-cutting or self-forming.

Screw connection according to any one of claims 1-8, characterized in that the diameter (Dg) of the threadless shaft section (40) is at most equal to the core diameter (Dk) of the thread (36).

Screw connection according to any of claims 1-9, characterized in that the shank (23) of the screw (30) has a conical connection (33) to the head (34) of the screw (30).

Screw connection according to claim 10, characterized in that the bore (12) of the disc (14) is adapted at least in the non-mounted state of the disc (14) to the tapered connection (33) of the shaft (32).